She told me all about Will, and what Liam did to him, and I told her my theory that Liam had murdered my mother and my cat. Mia’s hunger for revenge fuelled my own. Every day that we plotted I grew stronger, imagining my freedom. Things improved when Mia, pretending to be me, registered at a new GP surgery and managed to get me a prescription for anti-depressants and the pill, which she slipped me and I kept hidden in a box of tampons.

We arranged to communicate once we were on the island via cryptic notes left beneath a pile of stones on the beach resembling a cairn, something I built on the first day there and which I told Liam was a memorial for my mum. Whenever one of us had a message we would replace a stone from the top of the pile to signal the other person. Mia also left a note in the guest book – a deliberate coded message for Liam – which he didn’t get, but which made me smile.

‘Stay was cut short unfortunately, but it was wonderful until then. Tried looking for the burial site but couldn’t find it. I look forward to visiting in the future. A warning to guests; stay away from the cliffs. A fall could be fatal.’

She was referring to her life with Will being cut short, and referring to her own burial site, the ditch Liam left her in. She warned us away from the cliffs because at the bottom of them was the cave where she was camping out, hiding, waiting to put our plan into action.

The satellite phone in the cottage was my idea, to make sure Liam didn’t get suspicious from the very beginning, but we made sure that we took the charger out of the box. I have to say I enjoyed watching Liam’s frustration when he realised we had no means of escape and no one to call for help. It was beyond satisfying to see him going through just some of the terror he made me feel every day.

I used the cairn to warn Mia that there was a fourth, unexpected stranger on the island. I hadn’t been able to believe it at first – the chances of it seemed so impossible – and it wasn’t until Liam and I found the squatter’s campsite in the castle that I put it together and realised we weren’t alone.

I wanted to pull the plug immediately on our plans and left another note for Mia in the cairn, but she wouldn’t have it. We’d come this far, and she thought it worth risking it. She believed whoever was holed up in the castle would leave us alone, not wanting to get caught. And they did leave us alone. The problem was that Liam thought that they were the person who had stood at the window watching us; that they were responsible for the etching of the word ‘DEVIL’ on the window and the electricity being cut and the food being stolen and the woodpile being wrecked, when in fact it was Mia who had done it all. When I lay in bed listening to her scratching the word ‘DEVIL’ into the window downstairs, I was terrified that Liam would wake up and catch her. I couldn’t sleep for fear he was on to us.